The current chelation therapy has several drawbacks, including lack of selectivity, which could lead to trace metal depletion. Consequently, the proper function of metalloenzymes can be disrupted. Flavonoids possess chelating properties and hence interfere with the homeostasis of essential metals. We focused on zinc, an important trace metal required for the function of many enzymes and transcription factors. After making an initial evaluation of the Zn2+-chelating properties of a series of flavonoids, the effect of these compounds on various zinc-containing enzymes was also investigated. We performed enzyme inhibition assays spectrophotometrically using yeast and equine alcohol dehydrogenases and bovine glutamate dehydrogenase. Nine of the 21 flavonoids tested were capable of chelating Zn2+. Baicalein and 3-hydroxyflavone were the most potent Zn2+ chelators under slightly acidic and neutral pH conditions. This chelation was also confirmed by the ability to reverse Zn2+-induced enzymatic inhibition of bovine glutamate dehydrogenase. Although some flavonoids were also able to inhibit zinc-containing alcohol dehydrogenases, this inhibition was likely not caused by Zn2+ chelation. Luteolin was a relatively potent inhibitor of these enzymes regardless of the presence of Zn2+. Docking studies confirmed the binding of active flavonoids to equine alcohol dehydrogenase without any significant interaction with the catalytic zinc.

The Department of Chemistry Faculty of Science The University of South Bohemia in České Budějovice Branišovská 1760 37005 České Budějovice Czech Republic

The Department of Pharmacology and Toxicology Faculty of Pharmacy in Hradec Králové Charles University Heyrovského 1203 500 05 Hradec Králové Czech Republic

The Institute of Microbiology of the Czech Academy of Sciences Vídeňská 1083 142 20 Prague Czech Republic

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3-Hydroxyflavone is a mildly active and safe cobalt chelator while cobalt markedly enhances baicalein toxicity toward erythrocytes